The present invention relates to a drying and conditioning apparatus for tobacco and more particularly to an apparatus capable of adjusting the temperature and humidity of conditioning air.
In threshing leaf tobacco, excess moisture is given to the leaf tobacco so that threshing can be done to a satisfactory extent. The tobacco leaf (lamina) after threshing and separation from the vein is stored for ageing. In this case, since excess moisture was given to the tobacco leaf at the time of threshing as mentioned above, it is necessary to dry and condition the tobacco leaf before aging.
As an apparatus for performing such drying and conditioning operations, there has heretofore been known an apparatus having a drying chamber, a cooling chamber and a conditioning chamber, in which first tobacco leaves are dried in the drying chamber to a moisture content (7-10% DB) lower than a target moisture content (12-14% DB), then cooled in the cooling chamber and thereafter conditioned to the target moisture content in the conditioning chamber.
The reason why the tobacco leaves are dried to a lower moisture content than the target value and then cooled is that the air humidity in the conditioning chamber cannot be adjusted and it is around 100% RH.
In case the average moisture content of tobacco leaves after drying is set high, conditioning of the leaves with 100% RH air would cause some of the leaves to have higher moisture contents than a target value since the intermediate layer portion of each tobacco leaf is higher in moisture content than the other portion and there is a dispersion as a whole, and the growth of mold would result during aging. Such dispersion is decreased by lowering the average moisture content after drying, and since cooling causes lowering of the leaf temperature, the moisture content can be increased to a larger extent at the time of conditioning.
However, drying tobacco leaf to a moisture content lower than a target value, then cooling it and thereafter conditioning to the target moisture content, is a waste of heat energy.
If the temperature and moisture of conditioning air can be adjusted, the above problem will be overcome. As an apparatus for adjusting the temperature and humidity of air in the tobacco manufacturing field, for example, an apparatus having a steam atomizer and a cooler is known (see Japanese Patent Publication No. 13260/1982).
According to such known apparatus, however, it is impossible to adjust the temperature and humidity of conditioning air of about 40.degree.-70.degree. C. required for conditioning of tobacco leaves although it is possible to adjust the temperature and humidity of circulating air of about 20.degree. C.
For example, in the case of adjusting air of 20.degree. C., 50% RH to 60.degree. C., 60% RH, if steam is sprayed up to an absolute humidity corresponding to 60.degree. C., 60% RH, its amount becomes 0.0759 kg/kg'.
Absolute humidity of 20.degree. C., 50% RH . . . 0.0073 kg/kg' PA0 Absolute humidity of 60.degree. C., 60% RH . . . 0.0832 kg/kg' EQU 0.0832-0.0073=0.0759 kg/kg'
However, the enthalpy at 20.degree. C., 50% RH is 9.2 kcal/kg', and the enthalpy of steam to be sprayed is 49.0 kcal/kg' in the case of using saturated steam. On the other hand, the enthalpy at 60.degree. C., 60% RH is 66.3 kcal/kg'. That is, a heat quantity of 66.3-(9.2+49.0)=8.1 kcal/kg' is deficient. This quantity of heat is beyond the range capable of being made up for by the heat of adsorption of steam to the raw material or the heat generated by operation of a fan.
Therefore, it is impossible to reduce the heat energy by applying the above known construction to tobacco drying and conditioning apparatus.